Direction finding



Nov. 5, 1940. B. L. DOLBEAR ET AL 2,220,087

DIRECTION FINDING Filed July 7, 1956 2 Sheets-Sheet 1 INVENTORS B. L.DOLBEAR AND W- S WEBSTER.

ATTORNEY Nov. 5, 1940. B. DOLBEAR ET AL DIRECTION FINDING 2 Sheets-Sheet2 l -io Filed July 7, 1936 w AR 5am S Y O B E Mm: N E w W w I'- 5 A Y B8 v T.

"7 minations.

Patented Nov. 1940 NITED ST TEs V'PATENTQ: I OFFICE DIREGTIONFYIND'INGBenjamin L. Dolbear, Belmont, Mass, and William S.,Webster, Palmyra, N,J., assignors to Radio Corporation of America, a corporation of DelawareApplication July, 7,1936, Serial-No. 89,280

'9 Claims. (01. 250-11) This invention relates ,to novelimprovements inradio direction finder balancers and sense de-;

termining circuits and-is particularly adapted to direction findersoperating in the medium wave 3 length bands.

The object of this invention is t Smartypaproved directionfinderbalancers andsense de-v termining methods generally.

' Another object of this invention is to providea direction finderbalancer in which the degree of energy coupling from the open antennainto the loop circuit in. either direction is moreeasily controlled andwithout undesired coupling-being;

present. I e v A feature of this invention is the novel mechanicalarrangement of the coupling coil wheree vin the coil is moved from amaximum coupling position in one direction through a, minimum couplingposition, then to a maximum coupling position in the reverse direction.

Still another feature of this invention is the application of thebalancing operations tov only one side of a balanced loop circuitand-using the other side of the loop circuit In the art of radiodirection finding using a balanced rotatable coil or loop antenna, it iswell known that directional indications are muchv better defined whenthe rotatable loop antenna is used in a position of minimum signalpickup than when in the maximum position. Therefore, this invention isdirected to direction finder circuits employing, the minimum signalpickup and toimprove the desired nulls of the incoming signa iWhendirectionalreceiving antennae are employed at locations free fromsurrounding electrical conducting objects, such as might'exist in alarge open. field, it will be found that satisfactory null signal orbearing indications are usually obtainable. I v

. In many cases when thedirection finder. is used in the vicinity ofconducting objects such as steel'frame building, large trees, wires,masts,

metal stacks and; stays, the'null indications are indefinite'or obscuredue to a residual signal so that a desired complete null is neverevident. This phenomenon is known to be due usually to signal currentsset up in such nearby vertical conducting object's'which, although verysmall,

induce in the loop antenna spurious voltages that not only persist whenthe loop is in the null position, but such voltages are vectorially inquadrature phase with the desired voltages di'- rectly induced by thesignal in the'loop antenna.

for sense deter- One method of eliminating this, interfering residualsignal is to introduce into the loop circuit an equal and.opposite'voltage of proper phase to cancel out the spurious undesiredvoltage. v

Such voltage may be obtained from a vertical antenna which may be raisedin the vicinity of the direction finder and properly connected to acoupling system to transfer electrical energy into the loop circuit.

As the relative phase and magnitude of the rotation, it becomesnecessaryto provide means for varying bothdirection and amplitude of thecoupled voltage from the open antenna into the is to be described inthis application.

; The loop" antenna whenused alone will determine the plane ofpropagationof the signal but it does not discriminate between thecorrect bearing" of, the signal source and its reciprocal ,of'the samenull position, the loop voltagereverses -with respect to thenon-directional antenna voltage and-,a'difierential summation of the twovoltages resultsproducing a decrease in signal response from that of theloop alone. v I

As it"is customary-in most cases to tune the directional or loop'antenna to resonance inorder to benefittby the magnification of receivedsignal voltages, it is important that the circuit, of thenon-directional: antenna shall have the proper electrical constantstoprioducer the desired phase and amplitude;

spurious voltages changescwith the angle of loop loop circuit. A methodof accomplishing this I For correct functioning to balance out residual7 signal and clarify directional nulls, the open antenna voltageinduced.into the loop circuit must be ninety degrees out of phase'vectorially'with signal voltages picked up directly by the Y loop antenna.

On the other hand, for sense of direction de a termination, the openantennavoltagesinduced into theloop circuit must be either inqphase withthe loop signals or one hundred and eighty degrees out of phasevectorially.

For balancing purposes, the vertical antenna must be detuned from thesignal frequency a sufficient amount to produce the desired phasedifference.

For sense determining purposes, the open an tenna is tuned to the signalfrequency and its amplitude is controlled by resistance in the circuitresulting in the desired phase and magnitude of signal response.

The above described methods of producing desired effects in the circuitsare known in the prior art of radio direction finding and are describedin Keens Wireless Direction Finding, second edition, pgs. 65, 66 and6'7, and in a United States Pat. #1,868,982, issued to Fred H. Kroger.

This invention will best be understood by reference to the accompanyingdrawings, in which:

Fig. 1 shows a schematic wiring diagram of the loop and balancer circuitand the associated open antenna circuit coupled thereto;

Fig. 2 is an outline or front panel view of the balancer coupling coilin one of the maximum coupling positions;

Fig. 3 is a view similar to that of Fig. 2, except that the couplingcoil is in the minimum position;

Fig. 4 is an outline front panel View similar to Figs. 2 and 3, exceptthat the coil is shown in the other or reversed maximum position;

Fig. 5 is a plan View of the balancer rotor mechanism;

Fig. 6 is a front elevation of the balancer with the panel removed;while Fig. 7 is a, side view of Fig. 6.

Referring now to Fig. 1 of the drawings, the ordinary loop is shownindicated at I and is grounded at the central portion thereof. If it isdesired to isolate loop- I from any direct current it may be groundedthrough a condenser 2. The open antenna is indicated at 3 and isconnected to a variable tuning inductance shown in the form of avariometer 4.. An inductance coil 8 is provided to normally detune theantenna circuit when balancing operations are performed through couplingcoil II. Sense switch 5, is normally in the position shown, but whenoperated to give a sense of direction, connects the antenna 3 in serieswith resistance 6, which is included in the sense circuit to produce adesired phase difference and also to limit the amount of energy comingfrom antenna 3 to sense coil 1. Members 9 and ID are loop couplinginductance coils. Coil II] is coupled to a variable coupling coil II,this coil being arranged to slide and also rotate in a manner so as tocouple energy in either direction into the loop circuit. Coil 9 iscoupled to fixed coupling coil 1. This fixed coupling is employed fordetermining the sense of the line bearing. The switch 5 is arranged soas to transfer the open antenna 3 from normal connection with coil II tocoil 1.

Figs. 2, 3 and 4 show the panel arrangement of the principal elements ofthe improved balancer which comprise panel I2, operating knob I3 and apointer I4, the panel I2 being indicated at the top central portionthereof with the legend min. and at the right and at the left with thelegend max. Operating knob I3 is secured to a shaft I5 having locatedthereon a stop pin I6. The limit of motion is governed by pin I6stopping on stops ISA and I613. Stops ISA and IE3 are eccentricallylocated on member 22 and may be adjusted by a screw driver insertedinthe slot shown. The end of shaft I5 has located thereon a pinion gear2| which meshes with large spur gear I 1. A link I8 is pivotallyfastened to a second spur gear I9, gear I9 engaging a second pinion 20upon which the coupling coil II is secured. To more clearly indicate thecoil position with respect to the legends max. and min. on the panel, areference character X is indicated at one side of coupling coil I I.

The mechanical arrangement of the driving gears and linkage system forrotating coil II is shown in greater detail in Figs. 5, 6 and '7.Referring now to these figures, there is shown mounted on panel I2 ametallic supporting member 22 which is substantially T-shaped and issecured to the panel by three mounting bushings or spacing members 23and screws 24 and 25. At the lower end of mounting member 22 there islocated a bearing 26 for operating shaft I5, to which pinion gear 2I andknob 13 are secured. Shaft I5 is retained in operative engagement withbearing 26 'by means of a bushing 26A, a washer 21 and'a cotter pin 28.In the central portion of mounting member 22 a second bushing or bearing29 is provided for the shaft I4a for the large spur gear I1 and pointerI4. Links I8 and I8a are pivotally arranged by a pivot 30. Rivets 3|secure link I8 on the smaller spur gear I9. A cotter pin 3Ia. retainslinks I8 and |8a in operative engagement. The central bearing for gearI9 is arranged to move or slide along a fixed track comprising railmember 33 secured to mounting member 22 and having spring member 32riveted together by rivet 32A, the gear arrangement including gears I9and 20 and coupling coil II being supported on four movable carriagemembers 34 which are provided with four rollers indicated as 35.Variable coupling coil II is mounted on an insulating panel 36 and isarranged for rotation by being secured to a rotating shaft 31 by members38 and 39 which are securely bound together by screws 40. Shaft 31rotates within a bushing 45 which is secured between carriage members34. Pinion 20 is secured to shaft 31 by a pin 42, the teeth of pinion 20engaging the spur gear I9. Electrical connections are made from coil IIby means of flexible leads 43, 44 and 45. Lead 44 provides a tap on thewinding so that more than one frequency band can be covered with thesame coil. Loop coupling coils 9 and II) are supported from a staticshield 5I by a supporting strap 46 and spaced in their proper relationby spacing members 41. Strap member 46 is secured by means of spacers 48passing through screws 49 and 50 to a fixed support angle 52 fastened topanel 22 by means of a screw 53. Interposed between coils I I and 1 anddirectly in front of coils 9 and I is the static shield allowingmagnetic coupling to exist between coils I I] and I I .and between coils1 and 9.

In the operation of this device, when the pointer I4 is in the positionshown in Fig. 2, coupling coil II is at its maximum couplingpositionwith respect to coil I0. Upon rotation of the knob 13, coil I I isrotated and at the same time also moves away by angular movement of.link I8 from the vertical plane indicated in Fig. 2, and continues tomove away from coil Ill until it is in the minimum or horizontal planeshown in Fig. 3. After the pointer I4 passes the minimum position, thecoil II then starts returning toward coil I0, continuing in thismovement until the maximum position shown by pointer I4 in Fig. 4 isobtained.

It will be noted that this position is identicalsignalling betwen-sinpalace coilfansi I.

, rated so that, an- 1 4 edediflo 7,- i The o e mem e i t est ma e with"the signer and. induce'd'from'eoil'l'intocil dare inp a V a 'theJoopantennasl voltages. B'yproper rotati on of' "he o'op n nall' from thenull positio'r'ifthe sense of directionof the signal is now paragraph.

While only one modification of this invention is shown it is distinctlyunderstood that this ap- "plication should not'be limited to the deviceshown. I

What is claimed is:

1. A radio direction finder balancer comprising a loop circuit havingseparate fixed coupling coils connected to each side of said loopcircuit, an'antenna coupling coil coupled to one of the fixed coils ofsaid loop circuit, said antenna coupling coil being secured to. asupport member having mechanical means including ajlinkage systemwhereby said antenna coupling coil is arranged to'move along'its axisand rotate so tion or another into said loop circuit, a second antennacoupling coil, and aswitch and a resistance connected in series with anauxiliary antenna and said second antenna coupling coil.

2. A' radio direction finder balancer comprising a loop circuit havingseparate fixed coupling coils connected to each side of said loopcircuit, an

a resistance connected in series with an auxiliary antenna and saidsecondantenna coupling coil.

3. A radio direction finder balancer comprising a loop circuithavingseparate fixed coupling coils coupled to each side of said loop circuit,a fixed auxiliary antenna and a switching device, a fixed sense coilconnected through said switching device to said auxiliary antenna andcoupled to one of said separate coupling coils,- a balance'coil alsoconnected through said switching'device to said fixed antenna andinductively coupled, to

another of said separate coupling coils, and

" means for varying" the coupling between said i balance coil and atleast one of said separate coupling coils so as to couple energy in saidloop of said loop, a fixed-auxiliary antenna and a circuit in either onedirection or another.

' 4. A radiodirection finder, balancer system comprising a rotatableloopantenna having separate fixed coupling coils connected tov each side .75coupling coils, and separate means-for varying eemm tnei ii b M l pr sng a ta able 9i? an enn .ha ines aa e-fi ed swa -es" coils connedcdiio e-side easily determined as described in a foregoing as to variablycouple energy in'either onedirec- 70f? a d 1? nix d auxi iar an enn piltfiieqi se w sa d s r-i of said separate fixed coupling coils, a balancecoil inductively coupled to the other one of said, separate fixedcoupling coils, a fixed inductance coil connected in series with saidbalancecoil and said switching device to normally detune said auxiliaryantenna when said sense switch con nects said balance coil to saidauxiliary antenna, and means for varying the coupling between saidbalance coil and said last mentioned inductance I supporting memberhaving mechanical means whereby said antenna coupling coil is arrangedto move along its axisand rotate so as to variably couple antenna energyin either onedirection or another into said loop circuit, a secondantenna coupling coil, and a switch and a resistanceconnected in serieswith said antenna circuit and said second antenna coupling coil.

'7. A radio direction finder balancer comprising aloop circuit havingseparate fixed coupling'coils connected to each side of said loopcircuit, an antenna circuit having a coupling coil coupled. to one ofthe .fixed coils of said loop circuit, said antenna coupling coil beingsecured to a supporting member having mechanical means whereby saidantenna coupling coil is arranged to move. along its axis and rotatesoas to variably couple antenna energy in either one direction or anotherinto said loop circuit, a second antenna coupling coil, a switch and aresistance connected in series with said antenna circuit and secondantenna coupling coil, and a static shield interposed'between said fixedcoupling coils and said first and second mentioned antenna couplingcoils.

8. A radio direction finder balancer comprising a loop circuit, a fixedsupportpanel, a separate fixed coupling coil connected to each side ofsaid loop circuit and mounted on said fixed support panel, amovableauxiliary antenna coil located to be in coupling relationship withatleast one of said separate fixed couplingcoils, means for moving saidauxiliary antenna coil along its axisand also rotating it so as tovariablycouple energy in either one direction or" another into said loopcircuit, said means including asha ft,

a pinion gear secured to said shaft, a second gear meshing with saidpinion gear, a linkage member secured to said second gear, a thirdgearfor moving said linkage member, a fourthgear engaging said thirdgear, and an operating knob 9. A radio direction finder balancercomprising a loop circuit, a fixed support panel; a separate fixedcoupling coil connected to each side of said loop circuit and mounted onsaid fixed support panel, a movable auxiliary antenna coil located to bein coupling relationship with at least one of said separate fixedcoupling coils, means for moving said auxiliary antenna coil along itsaxis and also rotating it so as to variably couple energy in either onedirection or another into saidloop'circuit, said means including atrack, a carriage member having a plurality of rollers gear for movingsaid linkage member, a fourth 5 gear engaging said third gear, and anoperating knob secured to said fourth gear to vary the couplingrelationship between said movable auxiliary antenna coil and said fixedcoupling coil which is coupled thereto. 10

BENJAMIN L. DOLBEAR. WILLIAM WEBSTER.

